The invention refers to the field of optics (precisely to the methods and means of optical modification of electromagnetic radiation) and can be widely applied at forming of optical imaging of the objects (mainly of spatially extended ones) within incoherent light with the purpose of quality improvement of the perceived images.
According to the technical level common acknowledgement is attributed to the method of forming of an optical image in the incoherent light, which is based on the application of focusing optical elements (e.g. a biological subject""s lens or the objective of movie and photo cameras).
One of the ways of partial removal of the defects detected consists of diminishing the numerical aperture of the optical elements used (i.e. diminishing of the size of entrance pupil of the optical system). However, this method causes a decrease of illumination in the image formed, proportionally to the decrease of the entrance pupil""s area, as well as leads to lowering of optical system""s resolution in general.
Another method of object""s-optical image""s forming within incoherent light as well known from the technical level, is based on the change of transparency of the optical element in the direction from the center toward the peripheral area of the entrance pupil. In particular, in case of Gaussian law of transparency amendment, the dimensions of diffractive image of a point object decrease and consequently, resolution of the whole optical system increases and accordingly the quality of the formed image of original object improves. (J. Ojeda-Castaneda at ol., xe2x80x9cHigh Focal Depth By Apodiration and Digital Resporationxe2x80x9d, Appl. Optics, 27, No. 12, 1988; M. Mino, Y. Okano xe2x80x9cImprovement in the OTF of Defocussed Optical System Through the Use of Shaded Aperturesxe2x80x9d, Appl. Optics, 10, No. 10, 1971).
Nonetheless, similar to the cases mentioned above, the present method acknowledged from the technical level, decreases the impact of focusing errors only partially (in case of shifting of original object from the plane of optimal focusing of the optical system or in case of the said object""s extension along the optical axle of the system) due to certain extent of reduction of the formed image""s illumination.
We know another way of optical image forming of an extended object within incoherent light along with the device of realization that secures the feasibility to diminish the error of defocusing through implementation of light rays of the specific phase mask (U.S. Pat. No. 5,748,371).
The technical solution mentioned implies one or several lenses to form the image on the surface of optical-electronic converter. In the meanwhile, one of the main planes of the optical system has a cubic phase mask installed, by means of which optical transfer function is being changed (i.e. optical motion of the rays is being distorted) for the said system (that forms the image) so that it (optical transfer function) remains practically constant at defocusing of the optical system inside a relatively wide range. Further on, the formed distorted image is being fixed with the help of optical-electronic converter and the final image without any distortion is restored from it by means of accorded spatial filtration with assistance of a digital filter accomplished hardware-wise or in a numerical form through a PC.
The method and device for its implementation analyzed in the present report allow in the course of accomplishing procedure to decrease affecting of defocusing errors over the quality of object""s formed image as well as permit accounting and lowering of residual aberrations of the optical system.
Disadvantages of the quoted known technical solutions should be attributed to the higher requirements to the quality of optical-electronic converter because of the necessity to secure numeral ization of the signal in every particular point of the image not lower than 10 . . . 12 bits in order to receive high quality image. At the presence of noise of the receiver and/or at decreasing the number of quantization levels of the signal, the quality of restored image considerably deteriorates and the effect of depth enlargement of sharply imaged space is getting decreased.
Besides, in the known technical solutions analyzed above, the distortions of a point""s imaging brought in to the optical system by means of a cubic phase mask are defined by individual derivatives (conforming to the pupil coordinates) from the function of a (x3+y3) kind. It means that directions of the distortions mentioned to the considerable extent coincide with directions of distortions caused by the defocusing which leads to xe2x80x9csmearingxe2x80x9d of the restored image of the point source in case of shifting of the latter from the focus of optical system.
As the closest to declared subjects of the invention one might consider a method known from the technical level, dealing with forming of the optical image of an extended object within incoherent light and the device for its implementation that are based on the combined application of amplitude and cubic phase masks (U.S. Pat. No. 6,097,856).
According to this method the following procedures are accomplished in series inside the optical system equipped with at least one lens: pre-set distortion of the rays"" optical motion (i.e. modification of optical transfer function of the said system) by means of the amplitude-phase mask inserted to the system; optical-electronic conversion of the intermediate distorted object""s image formed by optical system and following deduction of distortions brought in by amplitude-phase mask and by optical system in general through accomplishing of accorded spatial filtration of the intermediate image mentioned afore.
A device meant to form optical image of an object within incoherent light (to implement the method described above) includes an optical system with at least one lens as well as the placed in series along the rays"" motion direction facility to distort the optical motion of the rays (i.e. to change the optical transfer function of the said system) in the form xe2x80x2of amplitude-phase mask, optical-electronic converter of the intermediate distorted image generated by optical system and finally a device for deduction of distortions brought in by amplitude-phase mask and optical system in general. The last named facility is digitally realized in the PC in form of totalized accorded spatial filter (used for the purpose of coordinated spatial filtration of distorted intermediate image). These technical solutions carry the same disadvantages as attributed to the method analyzed and the device for its implementation according to the U.S. Pat. No. 5,748,371.
It is worth emphasizing that every technical solution quoted above requires digital processing of the image formed that incurs additional computing devices and extra time to process initial data. Not only this complicates the structure of the optical system, but as well excludes the chance to receive a restored image in real time scale (meaning impossibility to apply the known technical solutions in the systems that require higher speeds of initial data""s processing).
In addition to that, distortions in the imaging of point light source, caused by insertion to the system of cubic phase mask (which function of phase delay looks like: xcex94"PHgr"=k(x3+y3)), are defined by individual derivatives of the mentioned function according to the pupil""s coordinates xe2x80x9cxxe2x80x9d and xe2x80x9cyxe2x80x9d, meaning that they are proportional to xe2x80x9cx2xe2x80x9d and xe2x80x9cy2xe2x80x9d. In the meanwhile, distortions brought in by defocusing are proportional to xe2x80x9cxxe2x80x9d and xe2x80x9cyxe2x80x9d accordingly and possess the identical direction.
In this regard, the quality of restored image considerably depends on the value of defocusing and consequently, it is not feasible to restore the ideal image of the source, especially in the case of a spatially extended object.
The basis of declared invention has been formed by the problem of creation of such a method of the object""s optical image generation within incoherent light along with device construction to realize the method, by means of which it would turn out possible to obtain in real time scale high quality restored image of the initial object that stays invariant regarding the defocusing.
The problem put with reference to the xe2x80x9cmethodxe2x80x9d subject of invention is being realized as follows. The method of forming of object""s optical image within incoherent light conforming to which below mentioned procedures are being accomplished in series inside the optical system equipped with at least one lens: preset distortion of optical motion of the rays by means of amplitude-phase mask inserted to the system; optical-electronic conversion of the formed distorted intermediate image and following deduction of distortions, brought in by amplitude-phase mask and by the whole optical system through performance of accorded spatial filtration of distorted intermediate image. In conformance to the invention, the pre-defined distortion of optical motion of the rays is being accomplished in the direction, which is close or identical to the orthogonal ones in regards to the distortions caused by defocusing and by aberrations of the optical system together with securing of rotary symmetry of the function of pre-set distortion.
It would be optimal if the ratio between meridional and sagittal components of the pre-defined distortion brought in to the motion of rays is set so that once the optical system has defocusings equaling by the absolute value with opposite marks, the points of light beams"" crossing (passing at the identical and/or at close value distances from the center of amplitude-phase mask) lie in the plane of optimal focusing of intermediate image in the circular zone of the circumference of the same radius the value of which exceeds the values of distortions caused by defocusing and by aberrations of the optical system inside the limits of each mentioned circular zones.
For the purpose of optical-electronic conversion of intermediate image it is expedient to apply an addressed optical spatial light modulator, while the accorded spatial filtration of such image within incoherent light should be carried out at the implementation of double optical-Fourier-transforming.
It is also reasonable in the course of forming of distorted intermediate image of the object through pre-set distortion of optical motion of the rays via amplitude-phase mask to impart circular rotary movement to the latter.
The problem put with reference to the xe2x80x9cdevicexe2x80x9d subject of invention (conforming to one of the construction variants) is being realized as follows. A device meant to form optical image of an object within incoherent light includes an optical system with at least one lens as well as the placed in series along the rays"" motion direction facility to distort the optical motion of the rays in the form of amplitude-phase mask, optical-electronic converter of the intermediate distorted image generated by optical system and finally a device for deduction of distortions brought in by amplitude-phase mask and optical system in general. According to the invention, in such a system the amplitude-phase mask is comprised of two coaxially and confocally installed lenticular screens with placing of lenses in each one of them along the concentric circles. Furthermore, at least one lenticular screen is mounted with secured option of a turn around the optical axle of the system to the angle regulated by the value of pre-defined distortion of the optical motion of rays of the said system.
The problem put with reference to the xe2x80x9cdevicexe2x80x9d subject of invention, conforming to another construction variant is being realized as follows. A device meant to form optical image of an object within incoherent light includes an optical system with at least one lens as well as the placed in series along the rays"" motion direction facility to distort the optical motion of the rays in the form of amplitude-phase mask, optical-electronic converter of the intermediate distorted image generated by optical system and finally a device for deduction of distortions brought in by amplitude-phase mask and optical system in general. Conforming to the invention, in such a system at least in one of the lenticular screens of the amplitude-phase mask, the lenses are made in the form of diffractive optical elements with strokes"" direction of diffractive structure close to the radial direction and with monotonous changing of the said direction and of the strokes"" frequency in proportion to the increase of distance from the center of diffractive element with the possibility to secure invariant status of the impulse response of the optical system with reference to defocusing. The strokes of diffractive structure of a diffractive element can be made with a triangular profile, the height of which is selected according to provision of securing the maximum diffractive efficiency of the mentioned structure.
The problem put with reference to the xe2x80x9cdevicexe2x80x9d subject of invention, according to one more construction variant is being realized as follows. A device meant to form optical image of an object within incoherent light includes an optical system with at least one lens as well as the placed in series along the rays"" motion direction facility to distort the optical motion of the rays in the form of amplitude-phase mask, optical-electronic converter of the intermediate distorted image generated by optical system and finally a device for deduction of distortions brought in by amplitude-phase mask and optical system in general. Conforming to the invention, direction of the strokes of diffractive structure of the optical element is determined by the equation of the following pattern:
"PHgr"="PHgr"i+kxcfx812, where:
"PHgr" and xcfx81xe2x80x94mean normalized polar coordinates in the plane of amplitude-phase mask;
"PHgr"ixe2x80x94means a polar angle that defines the direction of i-th stroke in the point of (coordinates) origin;
kxe2x80x94means a constant coefficient;
with the option of securing the invariant status of impulse response of the optical system with reference to defocusing.
In the present case the strokes of diffractive structure of diffractive element can be also made with a triangular profile, the height of which is selected basing on the provision of procurement of maximum diffractive efficiency of that structure.